Ghost Petpo cap repairs

I recently rented out a car from Europcar upon returning the car, the inspector released that the petrol cap falls out when you open it. They asked me to fill out a form to explain why it got detached. I explained that this was not tested upon picking up the car but found out about the issue after purchasing petrol. A day later I found out my refund has been withheld because Eurocar claims they need to repair the petrol cap. I then found out that the car is currently being renter out again. So the reason for my refund to be withheld is incorrect and also if the cap wasn't repaired mean the Eurocar new about the issue. All I need is my refund back. I've been calling the call centre with no success.